1. Field of the Invention
The present invention relates to a microwave air float bar for use in positioning, drying or curing of a continuous planar flexible material such as a web, web of paper, news print, film material, or plastic sheet. The present invention more particularly, pertains to a microwave air float bar whose pressure pad area includes a means of radiating radio frequency microwave energy to enhance accelerated ultraviolet heating of a web material to cause solvent evaporation, drying or curing. Microwave radio frequency energy in combination with columns of heated air impinging upon the web surface provides for concentrated heating of the web material thereby providing subsequent rapid evaporation, drying or curing from the surface of the material.
2. Description of the Prior Art
Demand for increased production volume and production speed of web material in dryers has caused the processing industry to increase web speed on their production lines. Typically this speed-up requirement results in the dryer being inadequate in drying the web, because the web did not remain in the dryer adjacent to a series of air bars for a sufficient length of time to dry the web because of the increased web speed. The solution for adequate drying was to either replace the entire dryer with a longer dryer, or to add additional drying zones in series with a first dryer zone. This, of course, is expensive and often times not feasible due to a shortage of physical floor space.
The present invention overcomes the disadvantages of the prior art dryers by providing a microwave air float bar to replace existing air float bars in web dryers. In addition to air flow of dry air from the Coanda air flow slots at the upper and outer extremities of the air float bar, a magnetron is located between the Coanda air flow slots, and transmits microwave radio frequency electromagnetic radiation waves to the traversing web. The traversing web drying is accomplished by impingement of a combination of both heated Coanda air flow and microwave radio frequency electromagnetic energy radiation. The combined concentration of heat from the Coanda air flow and the microwave radio frequency electromagnetic energy radiation from the magnetron is of a sufficient magnitude which allows the web to dry at a higher speed than normal prior art speed.
To a limited extent, the use of microwave energy to improve dryer efficiency has been taught in the art. U.S. Pat. No. 4,234,775 issued to Wolfberg, et al. teaches a relatively modern technique. U.S. Pat. Nos. 3,739,130; 3,764,768; 3,725,627; and 3,851,132 issued to White, Sayer, Arai, and VanKoughnett, respectively, teach earlier methods. In none of these references is the microwave radiator combined with an air stream to support the web, as well as cool the microwave generator and further heat the web material.